Virtually all chemical, biological and biochemical research depends upon the ability of the investigator to determine the direction of her research by assaying reaction mixtures for the presence or absence of a particular chemical species within the reaction mixture. In a simple case, the rate or efficiency of a reaction is assayed by measuring the rate of production of the reaction product, or the depletion of a reaction substrate. Similarly, interactive reactions, e.g., binding or dissociation reactions are generally assayed by measuring the amount of bound or free material in the resultant reaction mixture.
For certain reactions, the species of interest, or a suitable surrogate, is readily detectable and distinguishable from the remainder of the reagents. Thus, in order to detect such species, one merely needs to look for it. Often, this is accomplished by rendering a reaction product optically detectable and distinguishable from the reagents by virtue of an optical signaling element or moiety that is only present or active on the product or the substrate. By measuring the level of optical signal, one can directly ascertain the amount of product or remaining substrate.
Unfortunately, many reactions of particular interest do not have the benefit of having a readily available surrogate reagent that produces signal only when subjected to the reaction of interest. For example, many reactions that are of great interest to the biological research field do not subject their reagents to the types of modifications that can give rise to substantial optical property changes. Researchers have attempted to engineer substrates, which give rise to optical property changes. For example, typical binding reactions between two molecules result in a bound complex of those molecules. However, even when one member of the binding pair is labeled, the formation of the complex does not generally give rise to an optically detectable difference between the complex and the labeled molecule. As a result, most binding assays rely upon the immobilization of one member or molecule of the binding pair. The labeled molecule is then contacted with the immobilized molecule, and the immobilizing support is washed. Following washing, the support is then examined for the presence of the labeled molecule, indicating binding of the labeled component to the unlabeled, immobilized component. Vast arrays of different binding member pairs are often prepared in order to enhance the throughput of the assay format. See, e.g., U.S. Patent No. 5,143,854 to Pirrung et al.
Alternatively, in the case of nucleic acid hybridization assays, researchers have developed complementary labeling systems that take advantage of the proximity of bound elements to produce fluorescent signals, either in the bound or unbound state. See, e.g., U.S. Pat. Nos. 5,668,648, 5,707,804, 5,728,528, 5,853,992, and 5,869,255 to Mathies et al. for a description of FRET dyes, and Tyagi et al. Nature Biotech. 14:303-8 (1996), and Tyagi et al., Nature Biotech. 16:49-53 (1998) for a description of molecular beacons.
As noted above, binding reactions are but one category of assays that generally do not produce optically detectable signals. Similarly, there are a number of other assays whose reagents and/or products cannot be readily distinguished from each other, even despite the incorporation of optically detectable elements. For example, kinase assays that incorporate phosphate groups onto phosphorylatable substrates do not generally have surrogate substrates that produce a detectable signal upon completion of the phosphorylation reaction. Instead, such reactions typically rely upon a change in the structure of the product, which structural change is used to separate the reactants from the product. The separated product is then detected. As should be apparent, assays requiring additional separation steps can be extremely time consuming and less efficient, as a result of losses during the various assay steps.
It would generally be desirable to be able to perform the above-described assay types without the need for solid supports, additional separation steps, or the like. The present invention meets these and a variety of other important needs.
The present invention provides methods, systems, kits and the like for carrying out a wide variety of different assays. These assays typically comprise providing a first reagent mixture which comprises a first reagent having a fluorescent label. A second reagent is introduced into the first reagent mixture to produce a second reagent mixture, where the second reagent reacts with the first reagent to produce a fluorescently labeled product having a different charge than the first reagent. A polyion is introduced into at least one of the first and second reagent mixtures, and the fluorescent polarization in the second reagent mixture relative to the first reagent mixture is determined, this fluorescent polarization being indicative of the rate or extent of the reaction.
Another aspect of the present invention is a method of detecting a reaction. The method comprises providing a first reagent mixture, which contains a first reagent having a fluorescent label. A second reagent is introduced into the first reagent mixture to produce a second reagent mixture. The second reagent reacts with the first reagent to produce a fluorescently labeled product having a different charge than the first reagent. A polyion is introduced into at least one of the first and second reagent mixtures and fluorescent polarization is compared in the second reagent mixture relative to the first reagent mixture.
A further aspect of the present invention is a method of identifying the presence of a subsequence of nucleotides in a target nucleic acid. The method comprises contacting the target nucleic acid sequence with a positively charged or substantially uncharged, fluorescently labeled nucleic acid analog in a first reaction mixture. The nucleic acid analog is complementary to the subsequence whereby the nucleic acid analog is capable of specifically hybridizing to the subsequence to form a first hybrid. The first reaction mixture is contacted with a polyion and the level of fluorescence polarization of the first reaction mixture in the presence of the polyion is compared to the level of fluorescence polarization of the nucleic acid analog in the absence of the target nucleic acid sequence. An increase in the level of fluorescence polarization indicates the presence of the first hybrid.
Another aspect of the present invention is a method of detecting the phosphorylation of a phosphorylatable compound. The method comprises providing the phosphorylatable compound with a fluorescent label. The phosphorylatable compound is contacted with a kinase enzyme in the presence of a phosphate group in a first mixture and then contacting the first mixture with a polyion. The level of fluorescence polarization from the first mixture in the presence of the polyion is compared to the level of fluorescence polarization from the phosphorylatable compound with the fluorescent label in the absence of the kinase enzyme.
A further aspect of the present invention is a method of detecting the phosphorylation of a phosphorylatable compound. The method comprises providing the phosphorylatable compound with a fluorescent label. The phosphorylatable compound is contacted with a kinase enzyme in the presence of a phosphate group in a first mixture. The first mixture is contacted with a second reagent mixture comprising a protein having a chelating group associated therewith, and a metal ion selected from Fe3+, Ca2+, Ni2+ and Zn2+. The level of fluorescence polarization from the first mixture in the presence of the second mixture is compared to the level of fluorescence polarization from the phosphorylatable compound with the fluorescent label in the absence of the kinase enzyme.
A further aspect of the present invention is an assay system comprising a fluid receptacle. The system contains a first reaction zone containing a first reagent mixture which comprises a first reagent having a fluorescent label, a second reagent that reacts with the first reagent to produce a fluorescently labeled product having a different charge than the first reagent, and a polyion. The system also includes a detection zone and a detector disposed in sensory communication with the detection zone. The detector is configured to detect the level of fluorescence polarization of reagents in the detection zone.
Another aspect of the present invention is an assay system comprising a first channel disposed in a body structure. The first channel is fluidly connected to a source of a first reagent mixture which comprises a first reagent having a fluorescent label, a source of a second reagent that reacts with the first reagent to produce a fluorescently labeled product having a different charge than the first reagent; and a source of a polyion. The system also includes a material transport system for introducing the first reagent, the second reagent and the polyion into the first channel and a detector disposed in sensory communication with the first channel. The detector is configured to detect the level of fluorescence polarization of reagents in the detection zone.
Another aspect of the present invention is a kit. The kit includes a volume of a first reagent which comprises a fluorescent label; a volume of a second reagent which reacts with the first reagent to produce a fluorescent product having a different charge from the first reagent; and a volume of a polyion. The kit also includes instructions for determining the level of fluorescence polarization of the first reagent, mixing the first reagent, the second reagent and the polyion in a first mixture, determining the level of fluorescence polarization of the first mixture, and comparing the level fluorescence polarization of the first reagent to the level of fluorescence polarization of the first mixture.
Another aspect of the present invention is an assay system for quantifying a reaction parameter which comprises providing a first reagent mixture. The first reagent mixture includes a first reagent having a fluorescent label. A second reagent is introduced into the first reagent mixture to produce a second reagent mixture. The second reagent reacts with the first reagent to produce a fluorescently labeled product having a different charge than the first reagent. A polyion is introduced into at least one of the first and second reagent mixtures. The system also includes a computer implemented process, comprising the steps of determining a first level of fluorescence polarization of the first reagent mixture; determining a second level of fluorescence polarization of the second reagent mixture; comparing the first and second levels of fluorescent polarization; and calculating the reaction parameter.